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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made April 27, 2017

 Days 3-7Days 8-14Prob. Days 8-14
Precipitation No HazardsNot Available
TemperatureNo Hazards
SoilsNot Available

Categorical Outlooks
Experimental Probabilistic Outlooks (Information)

Valid Sunday April 30, 2017 to Thursday May 11, 2017

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 27 2017

Synopsis: Mid-level low pressure is anticipated across the Central contiguous U.S. during the 3-5 day period, with a forecast tendency to lift northward, toward and over the Upper Great Lakes region. Surface low pressure near the Ozarks is forecast to intensify while similarly lifting northward toward the Great Lakes. Several types of hazards are predicted to accompany this low pressure system, given both large temperature differences and the influx of Gulf moisture. Uncertainty is high regarding the Week-2 circulation and its impacts to the contiguous U.S. Alaska is expected to experience periodic surface low pressure systems of seasonable strength moving across the Bering Sea and Gulf of Alaska throughout the outlook period.

Hazards Detailed Summary

For Sunday April 30 - Thursday May 04: The primary feature of interest during the 3-7 day period is an anticipated surface low pressure system which is forecast to track from the Ozarks northward across the Upper Great Lakes region, before exiting into eastern Canada. Several hazards are expected to accompany this system. The first is the potential for severe weather on Apr 30 across the Lower Tennessee Valley and central Gulf Coast region. The Storm Prediction Center (SPC) expects favorable vertical wind shear profiles and moderate instability within this environment for the formation of severe thunderstorms. Another anticipated hazard with this storm system is heavy rainfall across the east-central and northeastern CONUS. Northern sections of this area are predicted to receive between 1.5"-2.5" on Apr 30-May 1, while southern sections are expected to get between 3"-4". During the subsequent two-day period, May 2-3, the central Gulf Coast region is predicted to receive an additional 2"-3" of rain. This is due to the anticipated formation of a warm front over Texas. A third concern with the original low pressure system is for high winds (30 knots or greater) on the western side of the storm, from the south-central Great Plains northeastward across the Midwest and Upper Great Lakes region on Apr 30-May 1. A fourth potential hazard with this storm system is unseasonably warm air (much above-normal temperatures) on its eastern side, and unseasonably cold air (much below-normal temperatures) on its western side. The predicted region of much above-normal temperatures includes the Mid-Atlantic, central Appalachians, and Ohio Valley, where temperatures are forecast to range from 12-18 degrees above-normal on Apr 30. This generally means high's are anticipated to reach the mid-80's. On the western side of the storm, much below-normal temperatures are forecast for portions of the central and southern Rockies, and central and southern Plains on Apr 30. The highlighted area on the map represents an overlap between expected minimum temperatures in the 20's to low 30's (at or below freezing), and expected maximum temperatures at or below 50 degrees F.

Flooding is possible, likely, imminent, or occurring across the Carolinas and southern Virginia, the Lower Ohio Valley/Midwest, the south-central Mississippi Valley and parts of adjacent states, northern North Dakota, and parts of Idaho. A cold front which stalled across North Carolina and Tennessee this past week brought severe storms to the region, rainfall amounts of 2-10", and flash flooding.

Alaska is forecast to experience periodic low pressure systems tracking across the Bering Sea and Gulf of Alaska during the 3-7 day period. None of these systems are expected to be unusually strong for this time of year.

For Friday May 05 - Thursday May 11: Substantial uncertainty is apparent in the wide range of spaghetti map perspectives of the mid-level circulation over North America in Week-2. Some eastward progression of the circulation pattern is anticipated, with a trough predicted to approach the East Coast, a ridge over the Nation's midsection, and another trough entering the western CONUS. Given the expected progressive pattern, and the forecast of modest 500-hPa height anomalies, limited hazardous impacts can be discerned at this time.

A slight risk of much above-normal temperatures is forecast for approximately the western quarter of the CONUS early in the Week-2 period, in-between an approaching trough to the west, and a departing ridge to the east. The area of anticipated much above-normal temperatures indicated on the map is where the GEFS has at least a 20% chance of exceeding the 85th climatological percentile of maximum temperature. A slight risk of much below-normal temperatures extends from eastern North Dakota across the Upper Mississippi Valley, and the western and central Great Lakes region. Here low temperatures may fall below freezing, while the GEFS supports at least a 20% chance of being below the 15th climatological percentile of minimum temperature.

According to the U.S. Drought Monitor released on April 27th (using data through 8 AM EDT, April 25th), coverage of severe, or greater intensity, drought throughout the CONUS dropped slightly (from 1.44 percent last week to 1.07 percent this week). This is the lowest coverage of D2-D4 drought over the CONUS since the inception of the U.S. Drought Monitor in 1999.

Forecaster: Anthony Artusa


Click here to see a display of the GFS Ensemble Forecasts

Please consult local NWS Forecast Offices for short range forecasts and region-specific information.